1. Field of the Invention
The present invention relates to a simply constructed and inexpensive aircraft and more particularly to a simply constructed and inexpensive aircraft which maybe of the flexible wing type.
2. Description of the Prior Art
Flexible wing aircraft have been known for many years as exemplified in 1910 by the Edwards rhomboidal airplane and the Picat Dubreuil airplane, and in the 1920's by the Platz sailwing glider. It is to be understood that the term "flexible wing" refers to a wing having a flexible lifting portion made of material such as canvas, for example; the flexible lifting portion forms, when properly inclined to the relative wind, an airfoil curve in response to the pressure differential on its upper and lower surfaces. This wing is to be distinguished from the more usual rigid type wing formed by a frame covered with sheet metal in which the airfoil curve is maintained by the stiffness of the wing structure, even at zero relative wind. The early aircraft mentioned are of interest for their simplicity; however, these aircraft were not entirely aerodynamically sound or were difficult to fly.
Later inventors developed the modern version of the flexible wing aircraft where the wing might include a leading edge spar, a trailing edge cable and a tip brace. This is exemplified by U.S. Pat. No. 2,228,829 to E. P. S. Newman. Additional work has been done by F. M. Rogallo who has received a number of United States patents extending over two decades for various aircraft systems using flexible lifting surfaces.
In the 1960's and 1970's interest in flexible wing aircraft has continued, such as exemplified by U.S. Pat. No. 3,584,813 to T. E. Sweeney et al. Since about 1948, Sweeney and his associates at the Princeton University Department of Aeronautical Engineering have been developing flexible wing aircraft of the type having a leading edge spar, a trailing edge cable, and a bridle system for bracing the flexible wing. Another example of interest is U.S. Pat. No. 3,614,032 to T. H. Purcell which also illustrates a leading edge spar and a trailing edge cable between which is a flexible material having embedded stays or cables for stiffening purposes.
Nevertheless, in spite of the work that has been done, there remain control problems, e.g. flexible wing aircraft have been found to be prone to luffing at low lift coefficients. Luffing is a nautical term which denotes fluttering of a sail. Manufacturing and cost problems have also arisen since flexible wings appeared to require somewhat massive and heavy structures in order to withstand the tension of the trailing edge cable. It has been found that this tension must be relatively high to prevent excessive luffing and billowing of the sail. Excessive billowing is undesirable because it causes loss of lift and increased induced drag. Further, no one appears to have developed an aircraft which can be flown and easily controlled by an individual having little or no flying experience. Nor does it appear that anyone has developed an aircraft capable of sustained flight, yet limited performance for use as an amusement type device. The term "limited performance" as used herein is intended to mean an aircraft limited in such characteristics as altitude so that even a novice pilot would have difficulty hurting himself or the aircraft regardless of the pilot's handling of the aircraft. Thus the prior art has not indicated a truly simple yet easily flyable aircraft which is exceedingly safe to operate by one who has never flown before. The majority of the prior art patents relate to traditional type aircraft in which the wings are made of flexible material, or to aerospace systems in which weight and volume are critical factors so that foldable, flexible wings are suggested.